来自子查询的 MySQL GROUP_CONCAT

Question

我试图从外部查询中的每一行获取一个串联列表，但我在“where 子句”中得到未知列“outter_client” 我发现您无法访问外部来自子查询的变量，有没有办法在没有存储过程、 View 或临时表的情况下重新构造此查询并使其正常工作？

SELECT client AS outer_client, top_domain
FROM log
JOIN (
   SELECT GROUP_CONCAT(t.domain) AS top_domain 
   FROM (
      SELECT domain 
      FROM log
      WHERE client = outer_client 
      GROUP BY 1 
      ORDER BY SUM(bytes)
      LIMIT 5
   ) t
) k
GROUP BY client
ORDER BY SUM(bytes)
LIMIT 5;

Answer 1

我认为您希望根据字节数为每个客户端提供前五个域。您可以使用嵌套选择和 substring_index()/group_concat() 技巧来做到这一点:

select client,
       substring_index(group_concat(domain order by sumbytes desc), ',', 5) as top5domains
from (select client, domain, sum(bytes) as sumbytes
      from log
      group by client, domain
     ) cd
group by client
order by sum(sumbytes) desc
limit 5;